The present invention relates in general to the field of regional electrical power supply systems, and in particular to a new and useful scalable, general-purpose, power flow calculation method and system that reduces or eliminates non-converging power system voltage stability calculation issues using a new bus type. The system outperforms the conventional calculation method where the power flow solution diverges due to ill-conditioning at high levels of power transfer. The new system's reformulated power flow configuration provides a new parameterization to eliminate the ill-conditioning issue in the power system's voltage stability calculation, improving its overall performance and operational cost.
Voltage instability has been the cause of many major blackouts, impacting industrial and commercial activities, incurring major inconvenience and costs for energy users, and resulting in increased utility operation and restoration cost.
Regional energy users are often found in a load center. A load center is generally defined as a particular geographical area where load demand is high and has few local power plants to satisfy the local power demand. Because there are few local power plants to satisfy the demand, the load center is usually supplied by multiple transmission sources through a number of boundary buses, resulting in a high proportional amount of load demand being provided by external power systems, i.e. power generation plants, and heavy power flow on the interface transmission lines. Load centers are therefore more susceptible to voltage instability and are typically voltage weak areas. Therefore, monitoring voltage stability at load centers is important and necessary. By monitoring the voltage stability condition at load centers and taking timely control actions, voltage instability can be effectively limited.
The prior does not contain the concept of an AQ-bus for voltage stability analysis that is a major feature of the present invention. Known works use the conventional PQ-bus type which results in numerical ill-conditioning near the point of maximum power transfer. To mitigate this issue, homotopy-based methods were introduced in the early 1990s and developed into commercial software (i.e., CPFLOW). However, these methods introduce complexity and additional computation. They mitigate but do not resolve the ill-conditioning problem.
Published patent application US 2013/0218494 discloses a Continuation Power Flow Method (or CPFLOW) for tracing power system behavior and is incorporated herein by reference.
A method for voltage stability analysis of power systems is disclosed in U.S. Pat. No. 5,745,368.
U.S. Pat. No. 7,979,239 discloses a system and method for monitoring and managing electrical power transmission and distribution networks.
A stability transfer limit calculation in a power transmission network is disclosed by U.S. Pat. No. 5,566,085.
A voltage stability discrimination system for power systems is disclosed by U.S. Pat. No. 4,974,140.
Applications and methods for voltage instability predictor (VIP) is disclosed by U.S. Pat. No. 6,249,719 and U.S. Pat. No. 6,219,591.
Real-time monitoring of electric power system voltage stability margins is disclosed by published patent application: US20130066480.
Measurement based voltage stability monitoring and control is disclosed by U.S. Pat. No. 8,126,667.
Bus-type extended load flow (BELF) is disclosed in the prior art and is known to the person of ordinary skill in the art of this invention.
U.S. Pat. No. 8,326,594 discloses a power flow analysis for balanced power distribution systems.
U.S. Pat. No. 7,321,834 discloses a method for calculating power flow solution of a power transmission network that includes an interline power flow controller (IPFC).
U.S. Pat. No. 7,813,884 discloses a method of calculating power flow solution of a power grid that includes generalized power flow controllers.
U.S. Pat. No. 7,117,070 discloses a power flow controller responsive to power circulation demand for optimizing power transfer.
U.S. Pat. No. 7,177,727 discloses a method for calculating power flow solution of a power transmission network that includes unified power flow controllers.
Published patent application US2013/0204556 discloses a hybrid three-phase power flow analysis method for ungrounded distribution systems.
Yang-2011 is an article that disclosed efficient solution algorithms for computing fold points of power flow equations.
Chinese patent CN102545206 discloses a voltage source commutation-high voltage direct current (VSC-HVDC) power flow computing method based on automatic differential (AD) and reserving non-linear method.
Chinese patent CN103091581 discloses a limit capacity transmission calculation method based on voltage collapse indices.
Chinese patent CN103199525 discloses a power distribution network flow computing method based on equivalent node injecting current transformation.
Chinese patent CN103353921 discloses a method for determining power system parallel load flow based on heuristic automatic network partitioning.
Nabavi-Niaki-1996 is an article that discloses a steady-state and dynamic models of unified power flow controller (UPFC) for power system studies.
Published patent application US2012/0022713 discloses a power flow simulation system, method and device.
Published patent application US20130238148 discloses an interior point method for a reformulated optimal power flow model.
A need remained for an effective, useful, scalable, general-purpose, power flow calculation method and system.